Related substance tests are established after complete
impurity profiling of respective substane where as
Chromatographic purity demonstarte the actual amount of the
substance present with unknown impurities.
chromatographic purity means wich is not calculated by
diluted standard.ie,the purity is linear with
concentration.In genearally final drug products calculated
and quantyfied with their diluted standards this is called
as related substances mehod
Chromatographic purity means which will give area % of
active ingredients as well as known impurities & unknown
impurities with rference standard.Realated subsances are
may be organic,inorganic and residual solvents(may be
In Sample way, Related substance (RS) are associated with
Raw material (API/Excipients)that comes along with desired
raw material either known and/or unknown and Chromatographic
Purity means identified as known and unknown.
chromatographic purity is calculated by area normalisation
method it gives the percentage of the main product and
related substances by HPLC gives you the Impurity profile
(known + unknown impurity)present in the product.